Most two-wheel trailers involve a conventional pivot-type hitch such that the trailer does not identically track with the towing vehicle, particularly when backing up. Nevertheless there have been attempts to provide a two-wheel trailer which will track with the vehicle similar to a single-wheel trailer. For example, U.S. Pat. No. 2,475,174 (Boone), U.S. Pat. No. 3,033,593 (Zaha), U.S. Pat. No. 3,379,452 (Torrisi), U.S. Pat. No. 4,452,465 (Bourke), U.S. Pat. No. 4,305,602 (Ungvari), U.S. Pat. No. 4,512,593 (Ehrhardt) and U.S. Pat. No. 4,076,264 (Chatterley) all disclose two-wheel trailers employing some special arrangement, such as casters, a control linkage between the two caster wheels, and/or a dual or specialized hitch arrangement for effecting a rigid securement of the trailer to the towing vehicle. These latter patents have hence attempted to provide a structure so as to increase the control, and thus the tracking, of the trailer relative to the towing vehicle. These attempts, however, as evidenced by the complexities of the structures disclosed in these patents, and the fact that these structures still have undesirable characteristics, readily indicate the difficulty in providing a two-wheel trailer together with a hitch attachment therefore which will properly track with the vehicle movement, particularly when backing up.
More specifically, U.S. Pat. No. 2,475,174 to Boone discloses a trailer having a pair of caster-type wheels, with the trailer having a single central hitch for attachment to the towing vehicle. The trailer also has a pair of separate auxiliary connectors disposed on opposite sides of the hitch adjacent the ends of the vehicle bumper, which auxiliary connectors control a flexible cable linkage, which in turn controls the swivelling of the casters. This patent hence discloses a three-point hitch arrangement, and does not permit free swivelling of the casters, but rather provides a complex arrangement for controlling swivelling of the casters.
U.S. Pat. No. 3,033,593 to Zaha as mentioned above, discloses a trailer having a pair of caster-type wheels, a central hitch of conventional configuration, and a pair of sidewardly spaced tie bars so as to create a three-point connection. This hence rigidifies the trailer relative to the vehicle, but the side tie bars must be released when swivelling of the wheels and backing of the trailer is desired. Further, this three-point connection does not permit proper rolling movement of the trailer relative to the vehicle, such as may be necessary to compensate for irregularities in the highway.
U.S. Pat. No. 4,305,602 to Ungvari discloses a trailer having caster-type wheels, with the trailer having a dual hitch arrangement so as to rigidify the trailer relative to the vehicle. This double hitch arrangement, however, has several disadvantages. For example, the tow vehicle must be provided with a specialized tow bar which mounts hitch balls thereon. Further, the overall hitch arrangement does not permit or compensate for rolling movement of the trailer relative to the vehicle due to unevenness in the highway. This hitch arrangement also does not permit even weight distribution on the trailer or vehicle wheels.
U.S. Pat. No. 4,512,593 to Ehrhardt discloses two caster wheels joined together by drive sprockets and chains so that the caster wheels are constrained for simultaneous movement. The trailer also has two rigid tow bars which couple to sidewardly spaced hitch balls mounted on the tow vehicle. This arrangement possesses the same disadvantages mentioned above, and like Ungvari, does not permit relative roll between the vehicle and trailer.
U.S. Pat. No. 4,664,403 to Livingston is directed to a trailer hitch structure for coupling a double caster-type wheel trailer to a towing vehicle having a conventional hitch bar fixed thereto and projecting rearwardly thereof. A rigid vehicle connector has a front portion fixedly connectable to the hitch bar. The front portion connects to a transversely extending rear portion which extends generally parallel to the vehicle bumper. This rear portion mounts adjustable bumper elements adjacent the opposite ends thereof, the bumper elements being adjustable for engagement with the vehicle bumper. A crossbar is positioned adjacent but slightly rearwardly from the rear portion and is coupled thereto through a swivel structure which defines a horizontal roll axis which extends in the longitudinal direction of the vehicle. The crossbar mounts a pair of hitch balls adjacent the opposite ends thereof. The trailer has a tongue structure provided with a pair of sidewardly spaced couplers for releasable engagement with the hitch balls.